Presently used organic greases do not comply with the requirements for the protection of ingot molds and fail to assure high-heat-duty performance thereof due to low resistivity of such greases to high temperatures. There are also known to be in practice protective coatings of non-organic origin, such as silicate coatings, which are characterized by either their complex chemical composition or intricate coating technique which necessitates pre-heating of casting molds to relatively high temperatures on the order of 1200.degree. to 1300.degree. C.
For example, there is known in the art a silicate coating (cf. U.S.S.R. Inventor's Certificate No 211,754), comprising a vitreous component of the following composition, in percent by weight of the total weight of the coating: BaO, 12.5; SiO.sub.2, 15; B.sub.2 O.sub.3, 12.5; Na.sub.2 O, 37.5; Al.sub.2 O.sub.3, 22.5; and commercial alumina.
The ratio of vitreous component to alumina is 30 to 20% and 70 to 80%, respectively. Likewise, added to the composition of said coating in excess of 100% is graphite in an amount of 5 to 7%, fire clay in an amount of 4 to 8%, and alcohol-sulphite lye in an amount of 8 to 10%.
The coating of the Inventor's Certificate referred to above suffers from the following disadvantages:
the presence in its composition of vitreous component, the production of which requires installation of additional equipment (melting furnace, grinding, sizing and screening apparatus); PA1 multicomponent structure which complicates the production process; PA1 low mechanical strength and thermal stability because of insufficient reactivity of the vitreous component to commercial alumina; PA1 difficulties in ensuring production effectiveness, resulting from inability to easily set up the process of vitreous component fusion under conditions of metallurgical and machine-building plants; PA1 the presence of BaO in the composition of the vitreous component makes the coating toxic, which impairs health conditions at work.
In addition, the presence in the coating composition of critical and expensive materials such as B.sub.2 O.sub.3, alumina, and BaO, increases the coating production cost, which renders impossible its wide application.
There are also known protective coatings disclosed in U.S. Pat. No 3,509,936, U.S. Pat. No 3,396,935, Belgium Pat. No 661,520, Japan Pat. No 48-7566, which, judging by their specifications, should suffer from a common disadvantage, it being insufficient operating durability due to the presence of a crystalline component, expressed as SiO.sub.2 and ZrO.sub.2, which undergoes polymorphic transformations under the action of molten metal temperatures, followed by changes in their volume and low strength of adhesion to the mold surface due to the presence of colloidal silica sol in their composition.
Moreover, the presence of colloidal silica sol in the composition of the protective coatings of the patents referred to above complicates the process of their production and requires additional equipment. It should also be noted that the aforesaid sol is a rather specific material.
It is an object of the present invention to provide a protective coating for ingot molds, casting molds and cores, which exhibits higher mechanical strength after solidification and sintering, as compared to the prior-art protective coatings.
Another object of the invention is to provide a protective coating which shows improved adhesion properties enabling the coating, adhesively applied to the mold working surface, to effectively withstand the washing-off force created by the flow of molten metal.
Yet another object of the invention is to provide a protective refractory coating which possesses substantial heat-insulating capacity making it possible to reduce thermal shock both on the surface and within the body of a mold, and thereby to limit the intrusion of molten metal to the mold working surface, as well as increase operating durability of casting molds.
Still another object of the present invention is to provide a protective coating which exhibits higher thermal stability, higher softening point, said coating being practically non-toxic.
It is, therefore, an object of the invention to provide a protective coating which will make it possible to enhance labor productivity in the shops where mold composition for casting is prepared, and increase production capacity of such shops by introducing simpler operating techniques for preparing a refractory mass through elimination of such operations as cleaning and washing of ingot molds, as well as by prolonging the service life of the refractory mass, enabling several casting cycles for example, five or six casting cycles to be carried out with a single application thereof to the mold surface.
Still another object of the invention is to provide a refractory coating with high physical-and-mechanical characteristics which render it suitable for protecting bottom molds exposed to high mechanical and thermal shocks while molten metal is poured thereinto.
Yet another object of the invention is to provide a refractory coating which will allow a reduction in the number of surface defects when casting ingots and increase the yield of quality metal.
Still another object of the invention is to provide a refractory coating which, if applied to the mold working surface in a layer with a thickness thereof being controlled over the height of a casting mold, will ensure directed crystallization of metal and reduce defects in the ingot macrostructure.
It is also an object of the invention to provide a protective coating which does not include in its composition scarce, critical and expensive components, and which exhibits high operating efficiency, and is easy and inexpensive to prepare.
It is likewise an object of the invention to provide a protective coating of such a composition which will enable diffusion processes to take place at a casting temperature of molten metal, and substitution or iron atoms in the surface layer of a casting mold by the atoms of aluminum and boron, which substantially enhances durability of casting molds.
These and other objects of the invention are accomplished by the provision of a refractory coating for the protection of ingot molds, casting molds and cores, which includes fire clay, graphite, water glass, water and a glass-ceramic component, the latter being alumina-containing material in an amount of not more than a half the weight of the total mixture and containing not less than 70 wt.% of Al.sub.2 O.sub.3 (according to its chemical composition), the latter being in alpha form. The above-cited composition makes it possible to obtain a coating of high mechanical strength and with improved adhesion properties after its solidification and sintering, said coating being chemically inert to the molten metal and slag-resistant.
In accordance with an embodiment of the invention, there is proposed a protective coating for ingot molds, casting molds and cores, which includes the following components: alumina-containing material with not less than 70 wt.% (according to its chemical composition) of Al.sub.2 O.sub.3 being present therein in alpha form; boron-containing material wherein B.sub.2 O.sub.3 is present in an amount of not less than 15 wt.% (according to its chemical composition); soda ash; fire clay; graphite; water glass and water; said ingredients being present in the following amounts:
______________________________________ percent by weight of the total coating ______________________________________ Alumina-containing material with not less than 70 wt. % of Al.sub.2 O.sub.3 /according to its chemical composition/ being present therein in alpha form 20 to 48 Boron-containing material with B.sub.2 O.sub.3 being present therein in an amount of not less than 15 wt. % /according to its chemical composition/ 0 to 10 Soda ash 0 to 5 Fire clay 2 to 5 Graphite 1 to 4 Water glass 2 to 5 Water, the balance. ______________________________________
The herein proposed composition makes it possible to obtain a heat-resistant coating having higher softening temperature, and non-toxic.
In accordance with another embodiment of the invention a protective coating includes commercial-grade alumina as the alumina-containing material, and datolite concentrate as the boron-containing material, these and other ingredients contained in the coating composition being present in the following amounts:
______________________________________ Percent by weight of the total coating ______________________________________ Commercial-grade alumina 35 to 40 Datolite concentrate 5 to 7 Soda ash 2 to 4 Graphite 2.5 to 4 Fire clay 2 to 4 Water glass 2 to 5 Water, the balance. ______________________________________
Such a composition enables the obtaining of a protective coating which possesses substantial heat-insulting capacity, and enabling diffusion processes to take place at a casting temperature of molten metal, with substitution of the atoms of iron in the surface layer of a casting mold by the atoms of aluminum and boron, which substantially enhances durability of casting molds.
In accordance with still another embodiment of the invention a protective coating includes datolite concentrate of the following composition:
______________________________________ Percent by weight of the total concentrate ______________________________________ Boron anhydrite 15 to 16 Calcium oxide 34 to 35 Silicon oxide 40 to 45 Iron oxides 3 to 4 Aluminum oxide 1.5 to 2.0 Calcination losses 8 to 10. ______________________________________
Such composition makes it possible to obtain a coating which shows higher mechanical strength, as compared to the prior-art refractory coatings, after solidification and sintering thereof.
In accordance with still another embodiment of the invention a protective coating can be provided for permanent casting molds, comprising the following ingredients: fire clay; graphite; water glass; and water; wastes of chemical industry, such as catalyst wastes from the production of synthetic rubber; and a mineralizer selected from the group consisting of boron-containing materials taken singly or in combination, the mineralizer consisting of danburite concentrate, datolite concentrate, ascharite, boric acid, colemanite, pandermite, borocalcite, boronatrocalcite; said ingredients all being present in the following amounts:
______________________________________ Percent by weight of the total coating ______________________________________ Catalyst wastes from the pro- duction of synthetic rubber 20 to 31 Mineralizer, boron-containing material selected from the above-mentioned group 2 to 10 Fire clay 2 to 3 Graphite 1 to 3 Water glass 2 to 3 Water, the balance ______________________________________
The coating of the afore-cited composition exhibits high mechanical-and-physical characteristics rendering it especially suitable for use in protecting bottom molds which undergo severe mechanical and physical shocks during teeming of molten metal therein, as well as enabling the reduction of surface defects during ingot casting, and increasing the yield of end-use metal.
In pursuance of the above-mentioned object of the invention, the herein proposed refractory coating for permanent metal casting molds comprises catalyst wastes from the production of synthetic rubber of the following composition: Al.sub.2 O.sub.3 ; Cr.sub.2 O.sub.3 ; SiO.sub.2 ; CaO; MgO; Fe.sub.2 O.sub.3 ; and K.sub.2 O; said ingredients being present in the following amounts:
______________________________________ Percent by weight of the total catalyst waste material ______________________________________ Al.sub.2 O.sub.3, the base Cr.sub.2 O.sub.3 from 13 to 15 SiO.sub.2 from 6 to 9 CaO from 0.1 to 0.7 MgO from 0.06 to 0.2 Fe.sub.2 O.sub.3 from 0.2 to 0.6 K.sub.2 O from 0.5 to 0.7 ______________________________________
This protective coating makes it possible to enhance labor productivity in the shops where the mold composition for casting is prepared, and increase production capacity of such shops by introducing simpler operating techniques for preparing the refractory mass through elimination of such operations as cleaning and washing of ingot molds.
As a particular embodiment of the present invention, the herein proposed coating for casting molds and cores includes an abrasive slurry as the alumina-containing component and has the following composition: abrasive slurry; soda ash; fire clay; graphite; water glass; and water; said ingredients being present in the following amounts:
______________________________________ Percent by weight of the total coating ______________________________________ Abrasive slurry 38 to 48 Soda ash 1 to 5 Fire clay 2 to 5 Graphite 1 to 3 Water glass 2 to 4 Water, the balance ______________________________________
The coating of the herein above described composition possesses improved adhesion properties and, therefore, effectively withstands, after being affixed to the mold working surface, the washing-off force created by a flow of molten metal, said coating being free from critical and expensive materials, and easy to produce.
Alternatively, the protective coating of the invention may include the slurry of the following composition: calcium oxide; silicon oxide; aluminum oxide; magnesium oxide; titanium dioxide; said ingredients being present in the following amounts:
______________________________________ Percent by weight of the total weight of slurry ______________________________________ Calcium oxide from 8 to 10 Silicon oxide from 8 to 10 Aluminum oxide from 70 to 77 Magnesium oxide from 0.5 to 2 Titanium dioxide from 3 to 5 Calcination losses the balance. ______________________________________
Such a composition makes it possible to obtain a protective coating, which, if applied to the mold working surface in a layer with a thickness thereof being controlled over the height of a casting mold, ensures directed crystallization of metal and reduces defects in the ingot macrostructure.
The following examples show typical ways of carrying out the aims of the invention. It is understood, of course, that these examples are merely illustrative, and the invention is not limited thereto.
In accordance with the invention, there has been developed a protective coating of the following composition: commercial-grade alumina; datolite concentrate; soda ash; fire clay; graphite; water glass; said ingredients being present in the following amounts:
______________________________________ Percent by weight of the total coating ______________________________________ Commercial-grade alumina from 75 to 85 Datolite concentrate from 10 to 17 Soda ash from 5 to 8 in excess of 100%: fire clay from 4 to 10 Graphite from 5 to 10 Water glass from 5 to 8 ______________________________________
This coating underwent a mill trial.